Am I doing myself a disservice by mixing these subwoofers? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 9 Old 07-25-2018, 08:13 AM - Thread Starter
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Question Am I doing myself a disservice by mixing these subwoofers?

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I haven't shared pics of my dedicated HT build on this forum yet (will come soon, I still have to put on some finishing touches).

However, I'm currently running a 7.4.4 system; whereby 2 subwoofers are the 18" VBSS DIY builds powered by an iNuke nu3000DSP, and the 2 others are 12" D-box David 300 powered subwoofers.

You've probably never heard of the D-Box David 300s (understandable)... they were sold MANY years ago in Canada through Costco as budget speaker. These are just a carry over of my old media room (not dedicated theater). They're apparently rated for 300W and can supposedly go down to 25 Hz. On their own, they can get pretty distorted if pushed to high SPL, so I keep them turned up about half-way on the plate amp in the back. As a budget subwoofer, I couldn't really complain about their performance back then.

But seeing that my 18" VBSS's dig a lot deeper and certainly have A LOT more (clearer) output. Should I even bother keeping the powered 12" D-box subwoofers?

I've always followed the mantra of "more subwoofers = better, to even out the response".

As of right now, I'm running all 4 subs in a baffle wall behind my acoustically transparent screen. see attached pics. I have 3x Sentinal Fusion 15's for my LCR, the L and R channel are stacked on top the VBSS's on their side, and the 12" D-Box are on top of the L R channels.

Unfortunately, given my room dimensions, I can't even re-position the D-Box's to say, the opposite end of the room to help even out the response further. So my options are really only to keep them or get rid of them. But I'd rather not keep them if they are worsening the performance overall.

I've included a reference pic of the 12" D-box on top of the 18" VBSS for scale, and also the current setup in my baffle wall space.
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post #2 of 9 Old 07-25-2018, 08:33 AM
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Since everything is ported and they are free I say run em. Put em near field to get the most out of them? More doesnt hurt especially since you are not mixing ported and sealed, they should integrate nicely.

Quote:
I've always followed the mantra of "more subwoofers = better, to even out the response".
I agree.

- 6 BA CR6 array center channel, QSC AD-S82 L/R, 4 jbl 8330a surr , 8 jbl 12" subs w/Inuke 6000. JVC rs420, Denon x4000, Sony x800 -
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post #3 of 9 Old 07-25-2018, 10:25 AM - Thread Starter
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Originally Posted by trilkb View Post
Since everything is ported and they are free I say run em. Put em near field to get the most out of them? More doesnt hurt especially since you are not mixing ported and sealed, they should integrate nicely.
Thanks for the quick reply... this definitely offers some reassurance.

Certainly would not mix ported and sealed; agree with you there.

Unfortunately, running them nearfield is not an option due to the cabinet size and what space I (don't) have around my seating. I keep forgetting that I didn't post my build/specs on this forum yet, so you guys aren't familiar with my dedicated room.

In that case, I might just keep an eye out for a used third matching D-box David 300 subwoofer to place on top that center channel speaker and fill that gap in my baffel wall
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post #4 of 9 Old 07-26-2018, 10:12 AM
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Typically when you mix two subs of different capabilities, overall system performance is “dumbed down” to that of the lesser sub. Here’s a case study complete with measurement graphs.

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post #5 of 9 Old 07-26-2018, 10:40 AM
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ah man, bassthathz is going to have to get rid of like 30 subwoofers and keep his best 2.

I think placement effects peaks and nulls more then the amount of cones and how "good" they are. Perhaps the guy in those post that you linked didnt place things right and room modes messed with him?

Messing around with REW room calculator and adding in more and more subs I found quickly that placement could kill bass, as well as phase.
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post #6 of 9 Old 07-26-2018, 09:25 PM
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Quote:
Originally Posted by Wayne A. Pflughaupt View Post
Typically when you mix two subs of different capabilities, overall system performance is “dumbed down” to that of the lesser sub. Here’s a case study complete with measurement graphs.

Regards,
Wayne A. Pflughaupt
@Repooc , another "risk" in the scenario you have (mixing differently tuned vented cabinets) is that their differing phase may cause unwanted additions and cancellations at various frequencies.

I have a similar scenario to yours, and I've been lucky (using Sub EQ in MultEQxt32). But I will be replacing all four with a pair of custom MiniMarty builds down the road to eliminate that "risk" and expand performance.
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post #7 of 9 Old 07-27-2018, 10:07 AM
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It won't cost you anything (but time) to experiment. So I think you should at least try it and measure with and without.


But I tend to agree with Cam Man, whichever subs have the higher tuning frequency will introduce a phase shift that you may have to deal with.

I turn the sharpness on my TV all the way up, because that's how I like my picture... real sharp.


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post #8 of 9 Old 07-28-2018, 11:47 AM
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Quote:
Originally Posted by trilkb View Post
ah man, bassthathz is going to have to get rid of like 30 subwoofers and keep his best 2.
That will not be happening.

That said: In an "ideal universe" all the subwoofers would be the same, and all of them would be 115db/w/m instead of 88db/w/m and no cone-mass and infinite power-handling and all that pretend-think stuff. Unfortunately the universe isn't ideal. (It's God's way of saying he loves you... [he really does care, see!? ])

Different drivers and box-types and brands (or even models within the same brand) can-and-do have wildly different parameters and capabilities; and so their phase and group-delay and linearity and sensitivity and THD and thermal-handling and tuning's will be all over the map.

As you scale up the system, say 32 subwoofers: The applied-power needed to hit a given SPL continues to drop.
32 18's doing 1mm is the same SPL as 1 18 doing 32mm's. Yet 1mm is like 32watts, vs 32mm's being 3200watts or whatever...

With this reduced excursion and power, also lowers the THD and thermal-compression to nill. It also ensures that all the drivers are well-within their optimal operating parameters, say flat from: whatever hz to whatever hz. (and so BassThatHz isn't as crazy as you think he is? Who would have thunk it!!! )

Now if you only have 2 and they are both different, and your demands for SPL are high, it's gonna be FAR more noticeable. Like say a 98db/w/m woofer with a decently strong magnet vs a 86db/w/m woofer with a weaker magnet or high inductance. One set is gonna hit their limits well before the other:
Will it be a problem?
YMMV...
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Last edited by BassThatHz; 07-28-2018 at 12:04 PM.
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post #9 of 9 Old 07-28-2018, 04:24 PM
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Quote:
Originally Posted by Steve Kuester View Post
It won't cost you anything (but time) to experiment. So I think you should at least try it and measure with and without...

THIS^


Since you can't relocate them, measure with and without them, and with different delays and crossovers to see what works best.

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